Uniflow engine with fluid flow arrangement

ABSTRACT

A uniflow engine includes a cylinder having a cylinder wall, an inlet channel, an extension of a central axis of the inlet channel first intersecting the cylinder wail in a first portion of the cylinder and next intersecting the cylinder wail in a second portion of the cylinder opposite the first portion of the cylinder, an intake air gallery, the intake air gallery having a gallery wall and being in flow communication with the inlet channel, and a plurality of intake ports extending between the cylinder wail and the gallery wall, at least some of the intake ports having different areas at the cylinder wall measured perpendicular to longitudinal axes of the intake ports, and wherein an area of at least one in take port in the first portion of the cylinder is larger than an area of at least one intake port in the second portion of the cylinder.

BACKGROUND AND SUMMARY

The present invention relates generally to uniflow engines and, moreparticularly, to arrangements for scavenging of such engines.

Most ported engines, which typically operate on the 2-stroke cycle,induce a high degree of swirl to the incoming air charge in order tomaximize the available surface area of the intake port band for intakecharge flow, and therefore reduced pumping work, as well as to assurehigh turbulence for good combustion. However, imparting swirl to theincoming charge requires a certain amount of energy, increasing pumpingwork, results in high heat transfer to the cylinder walls, causes mixingof the fresh charge with the exhaust gases remaining in the cylinder,and may entrain lubricating oil from the walls, adversely affectingemissions. In addition, filling of a 2-stroke cylinder depends on thepressure difference between intake and exhaust ports (valves), not theabsolute flow restriction of the intake system, and intake port areasare often restricted to achieve a more favorable pressure differentialacross the cylinder.

Regardless of whether the engine is an opposed piston engine or a singlepiston engine, when the intake is at one end of the cylinder and theexhaust is at the other end, the cylinder and the engine are referred toas having a “uniflow” design or “uniflow scavenged” design, scavengingbeing the description of the process whereby intake gas displaces theexhaust gas from the cylinder under pressure supplied by external means.The typical structure and operation of opposed piston engines is shownin, for example, U.S. Patent App. Pub. US2013/0036999 which isincorporated by reference.

The gas exchange process in a 2-stroke engine/machine occurs when thecylinder is near its maximum volume, i.e. bottom dead center in aconventional single piston engine, and is driven by some external meansof creating a pressure difference between the intake and exhaustpassages. A process where the incoming charge air enters the cylinder atone end of the cylinder, and pushes the combusted gases through exhaustpassages in the other end of the cylinder can be realized by intakeports in a cylinder or cylinder liner that are uncovered by the piston,and poppet or other exhaust valves in the cylinder head in the case of aconventional single piston engine design, or by intake ports uncoveredby one piston and exhaust ports uncovered by a second piston in the caseof an opposed piston engine. In most ported 2-stroke engines, the intakeport can be in the form of a series of slots or holes more or lessequally distributed around part of the circumference of the cylinderbore, generally patterned or shaped so as to cause the intake air toswirl about the axis of the cylinder.

It is desirable to minimize the turbulence of the intake air entering aported cylinder in order to minimize heat transfer, minimize work neededto induce charge motion, and minimize mixing of fresh and burned gasesin order to more closely achieve “perfect displacement” scavenging.

In accordance with an aspect of the invention, a uniflow enginecomprises a cylinder having a cylinder wall, an inlet channel, anextension of a central axis of the inlet channel first intersecting thecylinder wall in a first portion of the cylinder and next intersectingthe cylinder wall in a second portion of the cylinder opposite the firstportion of the cylinder, an intake air gallery, the intake air galleryhaving a gallery wall and being in flow communication with the inletchannel, and a plurality of intake ports extending between the cylinderwall and the gallery wall, at least some of the intake ports havingdifferent areas at the cylinder wall measured perpendicular tolongitudinal axes of the intake ports, and wherein an area of at leastone intake port in the first portion of the cylinder is larger than anarea of at least one intake port in the second portion of the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention are well understoodby reading the following detailed description in conjunction with thedrawings in which like numerals indicate similar elements and in which:

FIG. 1 is a partially cross-sectional view of a portion of an opposedpiston uniflow engine according to an aspect of the present inventiontaken at section 1-1 of FIG. 2;

FIG. 2 is a partially cross-sectional view of a portion of a uniflowengine as shown in FIG. 1;

FIG. 3 is a partially cross-sectional view of a portion of a uniflowengine according to an aspect of the present invention wherein opposedpistons are at a point of minimum volume in the cylinder, and

FIG. 4 is a partially cross-sectional view of a portion of a singlepiston uniflow engine according to another aspect of the presentinvention.

DETAILED DESCRIPTION

FIGS. 1-3 shows a portion of a ported uniflow engine 21 with a fluidflow arrangement according to an aspect of the present invention. Theuniflow engine 21 can comprise an engine block 23 or other structure inwhich a cylinder 25 (i.e., at least one) having a cylinder wall 27 isprovided. The cylinder 25 is ordinarily circularly cylindrical, but mayhave other shapes. FIGS. 1-3 show an opposed piston engine 21, however,it will be appreciated that the invention is applicable to a singlepiston engine 21′ as seen in FIG. 4. The opposed piston engine 21 isshown with the cylinder oriented such that the intake is at the top andthe exhaust is at the bottom, while the single piston engine 21′ isshown with cylinder oriented such that the intake is at the bottom andthe exhaust is at the top, however, in either case, the orientation ofthe intake and exhaust at the top or the bottom may be reversed. Forpurposes of discussion, structures of the opposed piston engine 21 willbe described, however, it will be appreciated that such structures arealso applicable to the single piston engine 21′, except where otherwiseindicated.

An inlet channel 29 is provided, usually formed in the engine block,into which intake air (or air and fuel, or other gas—hereinaftergenerically referred to as “air”) is drawn and directed toward thecylinder 25. The inlet channel 29 may comprise plural channels. Anextension of a central axis AI of the inlet channel 29 first (in adirection of air flow) intersects the cylinder wall 27 in a firstportion 31 (FIGS. 1-2) of the cylinder 25 and next in a second portion33 of the cylinder opposite the first portion of the cylinder. The firstand second portions 31 and 33 may be but are not necessarily first andsecond halves of the cylinder 25. The central axis AI of the inletchannel 29 can define an acute angle greater than 0° with a longitudinalaxis AC of the cylinder 25 to facilitate providing an axial component tothe motion of the air entering the cylinder.

An intake air gallery 35 ordinarily extends around at least a majorityof a circumference of the cylinder 25, however, the intake air gallerymay comprise two or more galleries that may (or may not be) be separatedby a wall. The intake air gallery 35 has a gallery wall 37 and is inflow communication with the inlet channel 29. If plural channels 29 areprovided, they may be arranged to be in flow communication withrespective galleries 35 or portions of a single gallery at differentportions around the circumference of the cylinder.

A plurality of intake ports 39 a . . . 39 h extend between the cylinderwall 27 and the gallery wall 37. The intake ports 39 a . . . 39 h can beformed in a cylinder liner 41, an interior of which forms the cylinder25. While FIG. 2 shows fifteen intake ports, it will be appreciated thatany number of intake ports can be provided. At least some of the intakeports 39 a and 39 b have different areas at the cylinder wall 27measured perpendicular to longitudinal axes A39 a and A39 b of theintake ports. An area of at least one intake port 39 a in the firstportion 31 of the cylinder 25 is larger than an area of at least oneintake port 39 b in the second portion 33 of the cylinder. For example,the area of at least one intake port 39 a disposed in the first portion31 of the cylinder 25 can be larger than the area of another intake port39 b located substantially diametrically opposite the intake port 39 a.

The location and dimensions of the intake ports 39 a . . . 39 h isordinarily designed to facilitate directing an intake air charge so thatit enters the cylinder 25 in a way that achieves minimum turbulence(and, thus, causing less heat transfer to the walls of the cylinder,requiring less work to induce charge motion, and resulting in lessmixing of fresh and burned gases) while evenly filling the cylinderacross its diameter, and thus facilitating the creation of (as close aspossible to) a generally cylindrical volume that expands along the axisAC of the cylinder 25 to push out the spent gases with a minimum ofmixing or energy exchange. Ports on the back side of the cylinder 25,e.g., port 39 b, relative to the central axis AI of the inlet channel29, i.e., the second portion 33 of the cylinder, are ordinarily smallerthan ports on the front side of the cylinder, e.g., port 39 a, relativeto the central axis of the inlet channel, i.e., the first portion 31 ofthe cylinder, and are ordinarily fed from a portion of the intake airgallery 35 that has a reduced cross-section relative to portions of theintake air gallery closer to the ports on the front side of thecylinder. The ports on the back side or second portion 33 of thecylinder 25 are ordinarily primarily intended to cool the back side of apiston 43 in the cylinder and to create a small air curtain near thecylinder wall to facilitate completely filling the cylinder.

The piston 43 can also be shaped to facilitate creation of the generallycylindrical volume by sloping a face 45 of the piston so that a meanface 47 of the piston defines a non-zero angle with a planeperpendicular to a longitudinal axis AC of the cylinder 25. The lowestpart 49 of the mean face 47 of the piston 43, i.e., the part furthestfrom what shall be referred to as a position of minimum volume in thecylinder 51 (i.e., the part that extends the least into the cylinder),is adjacent the first portion 31 of the cylinder. The position ofminimum volume in the cylinder 51 is defined as the point in thecylinder 25, in a single piston arrangement (FIG. 4), at which thepiston is at top dead center or, in an opposed piston arrangement (FIG.3), at which the two pistons are closest together. A highest part 53 ofthe mean face 47 of the piston 43 closest to the position of minimumvolume in the cylinder 51 (i.e., that protrudes the farthest into thecylinder) is adjacent the second portion 33 of the cylinder 25.

Ordinarily, the total area of the intake ports 39 a . . . 39 h is chosento achieve the desired flow rate at a desired pressure change across theuniflow engine. The size of the walls (i.e., thickness between thecylinder wall 27 and the intake air gallery wall 37 and circumferentiallength of walls) separating the intake ports 39 a . . . 39 h issufficient to provide an acceptable level of mechanical strength for theintended operating conditions in the cylinder. The spacing of the intakeports 39 a . . . 39 h and, thus, the width of the intake ports, isordinarily chosen so that piston rings 55 (FIG. 1) on the piston 43 inthe cylinder 25 do not expand into the ports or catch on the end walls(top and bottom portions) of the ports when the piston passes back andforth across the intake ports. The length and position of the intakeports along the cylinder axis AC are selected to function together withthe piston, which acts as a valve, to achieve a desired opening andclosing profile, and to obtain a desired effective compression ratio ofthe cylinder.

It will be observed that, in FIG. 2, the intake ports 39 a and 39 b arenot exactly diametrically opposed from each other, however, the port 39b is disposed at about 170°-190° on the opposite side of the diameter ofthe cylinder 25 to the port 39 a. In the embodiment illustrated in FIGS.1-2, the intake air gallery 37 does not extend completely around thecircumference of the cylinder 25 but, rather, only around a majority ofthe circumference, with two ports 39 b defining ends of the gallery. Ifthe intake air gallery were formed so that it extended around an entirecircumference of the cylinder, the port of minimum area could bedisposed diametrically opposite the port of greatest area.

Areas of intake ports decrease in area from a maximum area of at leastone intake port 39 a closest to a center of the first portion 31 of thecylinder 25 to a minimum area of at least one other intake port 39 blocated substantially diametrically opposite the intake port 39 a. Whilethere are not necessarily intake ports between the ports 39 a and 39 b,there is ordinarily at least one intake port 39 c, 39 d, 39 e, 39 f, 39g, 39 h between the intake port 39 a and the intake port 39 b. Theintake ports 39 a . . . 39 h can be arranged symmetrically around thecircumference of the cylinder 25. The intake ports 39 a . . . 39 h canbe but are not necessarily spaced at equal angles around thecircumference. The intake ports 39 c . . . 39 h can have areas that arethe same as one or the other of the ports 39 a or 39 b, but ordinarilyhave an area or areas between the maximum area and the minimum area,with the areas ordinarily progressively decreasing in size from largestclosest to the intake port 39 a to smallest closest to the intake port39 b.

Longitudinal axes A39 a and A39 b of at least some of the intake ports39 a . . . 39 h can be substantially coincident with radii Ra, Rb (FIG.2) of the cylinder 25 that intersect respective ones of the at leastsome of the intake ports. Longitudinal axes A39 a . . . A39 h of atleast some, ordinarily most or all, of the intake ports 39 a . . . 39 hare substantially parallel, i.e., forming an angle of about 10° or less,to the central axis AI of the inlet channel 37. This facilitates causingmost of the intake air flow to enter the first portion 31 of thecylinder 25 while the smaller amount of flow that passes around to theports on the second portion 33 of the cylinder creates the small aircurtain near the cylinder wall to facilitate completely filling thecylinder. Longitudinal axes of some of the intake ports may benon-parallel to the central axis AI of the inlet channel, which may beuseful to create a desired flow in the cylinder. It will be observed,for example, that the longitudinal axis A39 f of intake port 39 f isless parallel to the axis AI of the inlet channel 29 than otherlongitudinal axes of other intake ports.

As seen in FIG. 1, the intake ports 39 a . . . 39 h are ordinarilylonger in a direction parallel to a longitudinal axis AC of the cylinder25 than in a direction of the circumference of the cylinder and aregenerally in the shape of elongated slots. Where the first portion 31 ofthe cylinder 25 is a first half of the cylinder or front of the cylinderclosest to the inlet channel 29, and the second portion 33 the cylinderis a second half of the cylinder on a back side of the cylinder relativeto the inlet channel, a greater number of the plurality of intake ports39 b, 39 b, 39 f, 39 f, 39 g, 39 g 39 h, 39 h may be disposed in thesecond half of the cylinder than the number of intake ports 39 a, 39 c,39 c, 39 d, 39 d, 39 e, 39 e in the first half the cylinder while, atthe same time, a total area of all intake ports in the first half of thecylinder combined may be greater than a total area of all intake portsin the second half of the cylinder combined. To achieve the minimumturbulence and keep the flow patterns in the cylinder 25 parallel, it isdesirable to fill each slice of the cylinder corresponding to the intakeports 39 a, 39 c, 39 c, 39 d 4, 39 d, 39 e, 39 e in the first portion 31of the cylinder proportionately. Thus, the intake port dimensions areordinarily proportional to the volume of the slice of the cylinder towhich it corresponds and, thus, the intake port 39 a most closelydirected toward the axis AC of the cylinder (and, thus, the widestportion of the cylinder in cross-section) is ordinarily larger than theothers. It will be appreciated that, in reality, the air streamsentering the cylinder 25 through the various intake ports 39 a . . . 39h may not reach completely across the cylinder due to factors such asinteractions with the walls, the piston surfaces, or the wall thicknessof the cylinder wall. Therefore, intake ports farthest away from thecenter axis, e.g., intake ports 39 b, 39 b, 39 f, 39 f, 39 g, 39 g 39 h,39 h, and proceeding around the back side of the cylinder may be angledor specially shaped, and in particular shaped to direct the air alongthe inside wall of the cylinder, to “fill in” relatively dead areas tocomplete the axial-moving charge air surface. While covering somewhatmore than 180° of cylinder liner, these intake ports will ordinarilyonly supply a relatively small amount of the total charge air.

A cross-sectional area of the intake air gallery 35 can decrease from alargest gallery area closest to the first portion 31 of the cylinder 25to a smallest gallery area closest to the second portion of the cylinder33. A portion 37 p of the gallery wall 37 closest to the position ofminimum volume in the cylinder 51 can define an acute angle greater than0° with the longitudinal axis AC of the cylinder to facilitate providinga desired direction of air flow into the cylinder 25. The intake airgallery 35 supplying air to the cylinder 25 does not, in general, directthe air flow toward the cylinder axis. To the extent that this occurs,it is primarily a consequence of the orientation of the intake ports andinteraction of air flow from the intake ports with the face 45 of thepiston 43. The primary purpose of the intake air gallery 35 is to supplya smooth, relatively non-turbulent flow of air in sufficient volume tominimize a pressure drop during scavenging so that the ports 39 a . . .39 h and piston face 45 can direct the air appropriately. The portion 37p of the gallery wall 37 may, however, have sloping or roundedtransitions into the intake air ports 39 a . . . 39 h to better utilizethe length of the intake air ports between the gallery wall 37 and thecylinder wall 27 add to an axial component to air motion before itenters the cylinder. This effect may be the same for all ports or mayvary to achieve the desired flow motion.

The engine 21 further can further comprise an outlet channel 57,particularly in an opposed piston engine, an exhaust air gallery 59extending around at least a majority of a circumference of the cylinder25, the exhaust air gallery having an exhaust air gallery wall 61 andbeing in flow communication with the outlet channel, and a plurality ofexhaust ports 63 extending between the cylinder wall 27 and the exhaustair gallery wall. The exhaust ports 63 of the plurality of exhaust portscan be spaced at equal angles around the circumference of the cylinder25 and can be of equal size, which can facilitate even removal of spentgases as they are forced toward the exhaust ports by the volume ofincoming air.

In the opposed piston uniflow engine 21, the piston 43 is an intakepiston, and the uniflow engine comprises an exhaust piston 65 disposedin the cylinder. The two pistons 43 and 65 are disposed in the cylinder25 to close the ends of the cylinder and define a chamber. The piston 43or pistons 43 and 65 are typically not flat surfaces but, instead, aresculpted in order to create a cavity that is more favorable forcombustion. In an opposed piston engine 21, the two pistons 43 and 65will ultimately come together in near proximity to each other at thepoint of minimum volume of the cylinder 51 near the center of thecylinder. The cavities sculpted in the pistons 43 and 65 together form adesired combustion chamber. In a single piston engine 21′ (FIG. 4),combustion occurs between the piston face 45′ and a cylinder head 77′.Angling the nominal separating plane or mean face 47 between pistons 43and 65 or the mean piston face 47′ (and possibly the cylinder head 65′)can facilitate redirecting the flow of the incoming charge from a radialto an axial direction.

As shown in phantom in FIG. 3, at least one fuel injector 67 can beprovided for injecting fuel into the cylinder 25. A portion of theexhaust piston 63 closest to the at least one fuel injector 67 caninclude a recess 69 (shown in phantom) to facilitate introducing fuelinjected by the fuel injector or, as seen in FIG. 3, to receive aportion 71 (shown in phantom) of the fuel injector 67 that extends intothe cylinder when the exhaust piston is at the position of minimumvolume of the exhaust piston.

Historically, diesel engine combustion chambers were characterized as“quiescent” or “high swirl”. In a quiescent chamber, air is introducedwith as little turbulence as possible, and mixing is accomplished byextremely high fuel injection pressure sprays. In swirl chambers, theintake air is intentionally caused to swirl in the chamber by offsettingthe intake ports to the cylinder, and by shaping the port runner wallsto induce swirl into the air before it enters the cylinder. This allowsair-fuel mixing with lower injection pressures. The combustion chambersaccording to the present invention might be characterized as“semi-quiescent”.

The combination of the geometries such as those of the inlet channel 29,the intake air gallery 35, the intake ports 39 a . . . 39 g, the pistons43 and 65, and the exhaust ports 63 can facilitate filling the cylinder25 with intake air through the intake ports 39 a . . . 39 g that arearranged in the wall 27 of the cylinder while pushing another gas (inthe case of an internal combustion engine, the exhaust, or “spent”, orburned combustion gases, from the previous cycle) out of exhaust ports63 in the cylinder. To achieve high power and good efficiency in aninternal combustion engine, the design goal is to provide as much freshintake air as possible in the cylinder, which implies also removing asmuch of the burned gas as possible at the same time. The maximumreplacement of the burned gas with fresh air occurs when the two can beprevented from mixing. The combination of the geometries of the inletchannel 29, the intake air gallery 35, the intake ports 39 a . . . 39 g,and the piston 43 facilitates introducing the fresh intake gas into thecylinder 25 in such a way as to create a create a plug of fresh gas,with a predominantly flat, non-turbulent boundary between it and theburned gas in the cylinder 25, that then expands evenly from one end ofthe cylinder, and displaces the burned gas evenly along the axis AC ofthe cylinder. The conditions that make this distinct boundary possibleinclude: 1) the pressure in the plug of intake gas being essentiallyconstant across the entire cross sectional area of the cylinder, fromedge to center; 2) the velocity vectors of the intake gas enteringthrough the various intake ports 39 a . . . 39 g being essentiallyparallel to each other, and normal to the boundary surface; and 3) therebeing little or no turbulent velocity components across the boundarysurface. The reduced turbulence can minimize heat transfer between theincoming air and the cylinder walls, thus increasing thermal efficiency,reduce mixing between the intake and combusted gases, resulting inhigher purity of charge, and more closely resembling what is considered“perfect displacement” scavenging for higher power density. With modernhigh pressure fuel injection systems, the charge motion needed forcomplete combustion can be achieved with injection spray without theneed for inducing swirl for mixing of fuel and intake air.

In the specific case of an opposed piston engine 21, the exhaust exitsthrough the exhaust ports 63 which are also in the wall 27 of thecylinder 25, but at an opposite end of the cylinder from the intake airports 39 a . . . 39 h. However, the exhaust gas could also exit throughpoppet valves or any other type of valves that might be placed in acylinder head or other location in or near the end of the cylinderopposite the intake air ports 39 a . . . 39 h, depending on the engineconfiguration.

The angled mean face 47 of the piston 43 can be beneficial because, ifthe intake air were to be introduced evenly around the entirecircumference of the cylinder 25, the streams of gas from opposite sidesof the cylinder would tend to collide at the center and create atumbling, turbulent motion that would then cause mixing of gases,reducing the effectiveness of the scavenging process somewhat. Byintroducing the intake air primarily directionally from one side (firstportion 31) of the cylinder 25, the angled mean face 45 of the piston 43can serve to: 1) turn the direction of the incoming air flow from agenerally radial direction toward a direction along the axis AC of thecylinder 25, normal to the desired boundary surface between the incomingair and the gases sought to be exhausted; 2) forms a wedge of incominggas to build an even pressure plug across the majority of the cylindercross section; and 3) helps direct the gas flows that are away from theprimary intake flow to also turn parallel to the cylinder axis, to fillin the fresh gas plug all the way to the edges of the cylinder.

Aside from the exhaust piston and related structure, the structuredescribed above with respect to the opposed piston uniflow engine 21 canbe applicable to a single piston uniflow engine 21′ as seen in FIG. 4.Instead of an exhaust piston and a plurality of exhaust ports, thesingle piston uniflow engine 21′ can include one or more valves 73′ foropening and closing an opening 75′ in the cylinder head 77′. A singlepoppet type valve is shown for purposes of illustration, however, itwill be appreciated that plural and/or other types of valves may beused. Otherwise, the single piston uniflow engine 21′ can havestructures corresponding to those of the opposed piston uniflow engine21, such as a cylinder 25′, an inlet channel 29′, an intake air gallery35′, intake ports 39 a . . . 39 h, and a piston 43′ with a mean face 47′disposed at a non-zero angle to a perpendicular of the axis AC of thecylinder 25′.

In the present application, the use of terms such as “including” isopen-ended and is intended to have the same meaning as terms such as“comprising” and not preclude the presence of other structure, material,or acts. Similarly, though the use of terms such as “can” or “may” isintended to be open-ended and to reflect that structure, material, oracts are not necessary, the failure to use such terms is not intended toreflect that structure, material, or acts are essential. To the extentthat structure, material, or acts are presently considered to beessential, they are identified as such.

While this invention has been illustrated and described in accordancewith a preferred embodiment, it is recognized that variations andchanges may be made therein without departing from the invention as setforth in the claims.

What is claimed is:
 1. A uniflow engine, comprising: a cylinder having acylinder wall; an inlet channel, an extension of a central axis of theinlet channel first intersecting the cylinder wall in a first portion ofthe cylinder and next intersecting the cylinder wall in a second portionof the cylinder opposite the first portion of the cylinder; an intakeair gallery, the intake air gallery having a gallery wall and being inflow communication with the inlet channel; and a plurality of intakeports extending between the cylinder wall and the gallery wall, at leastsome of the intake ports having different areas at the cylinder wallmeasured perpendicular to longitudinal axes of the intake ports, andwherein an area of at least one intake port in the first portion of thecylinder is larger than an area of at least one intake port in thesecond portion of the cylinder.
 2. The uniflow engine as set forth inclaim 1, wherein the area of at least one intake port disposed in thefirst portion of the cylinder is larger than the area of another intakeport located substantially diametrically opposite the at least oneintake port disposed in the first portion of the cylinder.
 3. Theuniflow engine as set forth in claim 1, wherein areas of intake portsdecrease in area from a maximum area of at least one intake port closestto a center of the first portion of the cylinder to a minimum area of atleast one other intake port located substantially diametrically oppositethe at least one intake port closest to the center of the first portionof the cylinder.
 4. The uniflow engine as set forth in claim 3, whereinat least one intake port between the at least one intake port closest tothe center of the first portion of the cylinder and the at least oneother intake port located substantially diametrically opposite the atleast one intake port closest to the center of the first portion of thecylinder has an area between the maximum area and the minimum area. 5.The uniflow engine as set forth in claim 1, wherein longitudinal axes ofat least some of the intake ports are substantially coincident withradii of the cylinder that intersect respective ones of the at leastsome of the intake ports.
 6. The uniflow engine as set forth in claim 1,wherein longitudinal axes of at least some of the intake ports aresubstantially parallel to the central axis of the inlet channel.
 7. Theuniflow engine as set forth in claim 1, wherein longitudinal axes of atleast some of the intake ports are non-parallel to the central axis ofthe inlet channel.
 8. The uniflow engine as set forth in claim 1,wherein the intake ports are longer in a direction parallel to alongitudinal axis of the cylinder than in a direction of thecircumference of the cylinder.
 9. The uniflow engine as set forth inclaim 1, wherein the first portion of the cylinder is a first half ofthe cylinder and the second portion the cylinder is a second half of thecylinder, and a greater number of the plurality of intake ports isdisposed in the second half of the cylinder than in the first half thecylinder.
 10. The uniflow engine as set forth in claim 9, wherein atotal area of all intake ports in the first half of the cylindercombined is greater than a total area of all intake ports in the secondhalf of the cylinder combined.
 11. The uniflow engine as set forth inclaim 1, wherein a cross-sectional area of the gallery decreases from alargest gallery area closest to the first portion of the cylinder to asmallest gallery area closest to the second portion of the cylinder. 12.The uniflow engine as set forth in claim 1, wherein a portion of thegallery wall closest to a position of minimum volume in the cylinderdefines an acute angle greater than 0° with a longitudinal axis of thecylinder.
 13. The uniflow engine as set forth in claim 1, wherein thecentral axis of the inlet channel defines an acute angle greater than 0°with a longitudinal axis of the cylinder.
 14. The uniflow engine as setforth in claim 1, further comprising an outlet channel, an exhaust airgallery extending around at least a majority of a circumference of thecylinder, the exhaust air gallery having an exhaust air gallery wall andbeing in flow communication with the outlet channel, and a plurality ofexhaust ports extending between the cylinder wall and the exhaust airgallery wall.
 15. The uniflow engine as set forth in claim 14, whereinexhaust ports of the plurality of exhaust ports are spaced at equalangles around the circumference of the cylinder.
 16. The uniflow engineas set forth in claim 14, wherein all exhaust ports of the plurality ofexhaust ports are of equal size.
 17. The uniflow engine as set forth inclaim 1, comprising a piston disposed in the cylinder, a mean face ofthe piston defining a non-zero angle with a plane perpendicular to alongitudinal axis of the cylinder.
 18. The uniflow engine as set forthin claim 17, wherein a lowest part of the mean face of the pistonfurthest from a position of minimum volume in the cylinder is adjacentthe first portion of the cylinder.
 19. The uniflow engine as set forthin claim 18, wherein a highest part of the mean face of the pistonclosest to the position of minimum volume in the cylinder is adjacentthe second portion of the cylinder.
 20. The uniflow engine as set forthin claim 17, wherein the uniflow engine is an opposed piston engine, thepiston is an intake piston, the uniflow engine comprising an exhaustpiston disposed in the cylinder.
 21. The uniflow engine as set forth inclaim 20, comprising at least one fuel injector for injecting fuel intothe cylinder, a portion of the exhaust piston closest to the at leastone fuel injector including a recess.
 22. The uniflow engine as setforth in claim 21, wherein at least a portion of the at least one fuelinjector extends into the cylinder, the portion of the at least one fuelinjector being disposed in the recess when the exhaust piston is at aposition of minimum volume of the exhaust piston.
 23. The uniflow engineas set forth in claim 1, wherein the intake gallery extends around atleast a majority of a circumference of the cylinder.
 24. The uniflowengine as set forth in claim 17, wherein the uniflow engine is anopposed piston engine, the piston is an intake piston, a second pistonis an exhaust piston, and the intake piston and the exhaust piston aredisposed in the cylinder and define an enclosed chamber.